Our house was built in 1997. The pipes are copper (including the city water supply pipe). Some time after the house was built, the previous owners installed a water softener. The softener parts are all plastic, so the city water supply is not part of the grounding path.

I dug up the installation manual for my softener (Kenmore Ultrasoft 100), and it says to bond the softener in/out pipes to provide a grounding path. This has not been done. It has been this way for ~10 years.

There is already a solid copper wire clamped to the cold water pipe that runs over to the breaker box. (This wire is attached to the plumbing after the softener.) Not sure the gauge of the wire. Presumably this wire grounds the cold water pipes. I would guess there is a grounding rod somewhere behind the breaker box, but I have not verified this.

Edit: Because of this grounding wire, it seems most of the cold water plumbing is already grounded. The only part that isn't bonded is the ~5ft of cold water pipe that comes into the basement before the softener.

I do believe my outlets are grounded because the "Ground" LEDs on all of my surge strips are lit.

Should I follow the softener manual's advice and bond the water softener in/out pipes?

If the breaker box is already grounded via a grounding rod, would this extra ground path hurt anything? It seems like a good idea to have second path, in case something happens to the first one.

However, I am not sure about the difference in potential between the two ground points. Could this cause a problem? (For reference, the cold water supply line is ~50ft from the breaker box.)

Follow-up question: Should I bond the hot water pipes to the cold water pipes? There seems to be some conductivity between the hot/cold pipes already (checked with a multimeter), but I can't find an actual bonding wire anywhere, so I may just be seeing some incidental conductivity via the water heater or faucets.

1 Answer
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It is important to understand the reason for grounding/bonding the water pipe system in a house. The ground of the electrical service panel is typically grounded via an 8 ft or more ground rod at the meter and/or panel AS WELL AS via a bonding conductor to the metallic water source pipe. (plastic feeds are not bonded). The grounding wire is typically #4 Copper. The grounding of the water pipe is not necessary for the proper grounding of the electrical system if there is a separate earth ground supplied,(ground rods, etc) however it is necessary in order to assure an equal ground potential between the electrical system and metallic plumbing system. The reason for having both the electrical and plumbing bonded at the same potential is to eliminate any possible voltage potential between the two when electrical appliances that contact water are used. IE: electric water heaters, ice makers in fridge, garbage disposals, etc., and any accidental contact of voltage to the water system. If this was not done, it may be possible for voltage to appear on the plumbing fixtures. Regarding your first question about bonding the two sides of the water softening system, the recommended bonding is to assure the upside metallic system is at the same ground potential as the downside piping, for reasons described above.

But if the cold water pipe is currently connected to the electrical system, aren't they already at the same ground potential? Will adding the 2nd ground path be a problem?
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msemackMar 8 '11 at 12:11

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@msemack - You are not adding a second ground path, you are making sure the output plumbing (plumbing after softener) is also at ground potential. Think of the softener system as a break in the circuit, by bonding the in and out together you are completing the circuit. So by doing this you are making sure the entire system is at ground potential.
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Tester101♦Mar 8 '11 at 13:03

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The really short answer is "bond the grounds from everything to everything else with the biggest conductors you can afford". The better a job that you do at that, the less likely you are to have voltage differentials that can shock/kill you or damage your equipment.
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Brian KnoblauchMar 8 '11 at 13:46

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@msemack- I think you are confusing bonding isolated metallic tubing with the actual earth ground at the panel and water inlet pipe. The plumbing system is not, nor ever connected to the electrical system, it is simply connected at earth ground so that it will not become connected to any "hot" electrical potential.
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shirlock homesMar 8 '11 at 22:14

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@msemac- You don't need two ground rods. The metal pipe that leaves your house is buried,right? that is a very good ground. Now regardless if there is a wire to a ground rod from your panel you still need to bond the ground buss of the panel to the water inlet before the meter to assure no difference in potential between the two differently grounded systems. The OHMs of the two separately can be different, that creates potential, bonding them together equals the conductivity/OHMS. BTW you can't measure it with a std ohm meter, you need to use a Megger.
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shirlock homesMar 9 '11 at 23:03